The present invention relates to a transfer device associated with a power transmission unit for automotive vehicles of front and rear wheel drive type, and more particularly to a transfer device of the type which includes an input shaft for connection to an output shaft of the transmission unit, a first output shaft axially aligned with the input shaft, a second output shaft located parallely apart from the input and first output shafts, and a selector gear unit for selectively completing low and high speed gear trains among the input shaft and the first and second output shafts.
In general, as is seen in FIG. 7, a conventional transfer device of the type includes an input shaft 1 for connection to an output shaft of a power transmission unit, a first output shaft 2 coaxially connected at its inner end with the input shaft 1 by means of a bearing to permit relative rotation of the shafts 1 and 2, and a second output shaft 3 located parallely apart from the input and first output shafts. A high speed drive gear 1a is integral with the input shaft 1 and in mesh with a high speed counter-gear 4a on a countershaft 4. The high speed counter-gear 4a is permanently meshed with a high speed output gear 3a rotatable on the second output shaft 3, the output gear 3a having the same number of teeth as those of the high speed drive gear 1a. A low speed drive gear 2a is freely rotative on the first output shaft 2 and in mesh with a low speed counter-gear 4b on countershaft 4. The low speed counter-gear 4b is permanently meshed with a low speed output gear 3b rotatable on the second output shaft 3, the output gear 3b having the same number of teeth as those of the low speed drive gear 2a.
The transfer device further includes a first selector gear unit 5, which is coaxially arranged with the input and first output shafts to selectively connect the first output shaft 2 with the low and high speed drive gears 2a and 1a, and a second selector gear unit 6, which is coaxially arranged with the second output shaft 3 to selectively connect the second output shaft 3 with the low and high speed output gears 3b and 3a. To drive the front and rear wheels at a low speed, both the selector gear units 5 and 6 are shifted to connect the first output shaft 2 with the low speed drive gear 2a and to connect the second output shaft 3 with the low speed output gear 3b. To drive the front and rear wheels at a high speed, both the selector gear units 5 and 6 are also shifted to connect the first output shaft 2 with the high speed drive gear 1a and to connect the second output shaft 3 with the high speed output gear 3a. For switching-over the front and rear wheel drive to the rear wheel drive, only the second selector gear unit 6 is returned to its neutral position.
In such a transfer device as described above, the second selector gear unit 6 is located apart from the first selector gear unit 5. As a result, the shifting mechanism for the selector gear units is complicated in construction and occupies a large space within the transfer device. Additionally, when the transfer device is shifted from the rear wheel drive to the front and rear wheel drive or from the low speed range to the high speed range, both the first and second selector gear units must be shifted at the same time. Furthermore, during operation of the transfer device, all the gears 1a, 2a, 3a, 3b, 4a and 4b are always driven to cause unnecessary torque losses by stirring of lubricating oil and frictional resistances.